Slow running g4

Hi there, i hope anyone out there can help me!!
I have a Imac g4 800 17" and its running really slow.
I have just purchased it from an auction and they can't remember the Admin user name so am unable to update or make changes to the system. also after about 5 mins after logging on the coloured sphere appears and will stay on for ages. i have also reset the memory from the underside panel.

Please help, oh and whats the OS limit that can be installed on the g4? many many thanks.

How slow is "really slow"? I only ask since that's an old machine and the specs are relatively limited compared to more modern machines.

I'll let someone who knows more about older Macs chip in but I believe the newest version of OS X you can run will be 10.4.11.

i can login, but after that the sphere will stay on for, i counted 15 mins before i turned it off. all i know is its got a superdive and a 17" flatpanel monitor. i can open the settings menu and again freezes until its turned off. it didnt come with a apple keyboard so am using a third party one

Did the machine come with install discs? If so, you should probably wipe it clean if it's a new machine (new to you at least). That way, you can get rid of all the junk that came with it and start fresh. If you didn't get the discs, contact the auction house and ask if they have them.

sorry it didnt, plus i wouldnt know how to reinstall incase it asks for the admin password and user name whick i dont have.

MacTracker says that OS X 10.4 (Tiger) is indeed the latest version you can run. The last time I looked retail packages (Black Disks) were running about $80 USD.

Install of the OS is easy and does not require the Admin password. Boot from the OS disk, go to Disk Utility and format the drive then install the OS.

thats great cheers, one more thing. how do i reset the memory as i am a third party keyboard and not a mac keyboard? cheers